Ambulatory infusion systems are known in the art for a variety of applications. In particular, ambulatory infusion systems adapted for insulin administration form a basis for state-of-the-art therapy of diabetes mellitus by CSII (Continuous Subcutaneous Insulin Infusion). These systems are typically computer controlled micro-dosing pumps that are adapted to be worn continuously and concealed from view. The insulin is infused via a subcutaneous cannula that is replaced by a user, e.g., a PwD (Person with Diabetes) or a relative of such a person, every few days. Such insulin pumps are commercially available from a number of suppliers.
Insulin pumps are typically designed to infuse an insulin formulation or another liquid drug continuously according to a basal administration profile that is variable over the time of day. In addition, infusion pumps are often designed to infuse larger drug boli in a comparatively short time interval on demand. In CSII, insulin boli are typically administered to compensate food intake and to lower an undesirably raised blood glucose level. The total daily amount of infused insulin may vary depending on personal factors and habits of a PwD in a considerable range (between, e.g., 10 IU to 80 IU, with 100 IU (International units) corresponding to 1 ml of a liquid insulin formulation for the currently most common concentration of liquid insulin formulations).
CSII therapy may be used in the field of application. Phrases like “infusion system” or “infusion device” may therefore refer to systems and devices which are suitable for CSII and similar applications, such as various hormone therapies, pain therapy or cancer treatment.
Infusion systems may include a positive-displacement pump of the syringe-driver type coupled to a cylindrical drug cartridge out of which a liquid drug formulation is forced into an infusion line by displacing a cartridge plunger in a controlled manner. Reference is made to WO 2003053498 A2 and WO 2000025844 A1 regarding the design and features of a state-of-the-art infusion pump. However, the present disclosure is not limited to a specific therapy or system design.
While complete filling of the drug containers is generally desirable, some air typically remains in a drug container and is subsequently infused into the body along with the liquid drug. This holds especially true if the drug cartridge is not filled by a trained and experienced professional and under well-controlled conditions, but is filled by a user at home as it is typically the case in CSII therapy. In addition, some air is typically dissolved in a liquid insulin formulation which outgases during application, thus forming air bubbles. The infusion of air, however, is generally undesired. Furthermore, it is disadvantageous if a pressure sensor is used in the system for detecting blockages and/or occlusions as will be discussed below in more detail, wherein it may be desirable to remove the air from the drug stream prior to infusion into the body.
U.S. Pat. No. 7,238,224 discloses a degassing device that may be used for removing gas, e.g., air, from a liquid. The device includes a chamber with an inlet as well as a hydrophilic membrane and a hydrophobic membrane which are arranged at opposing walls of the chamber. If a mixture of liquid and gas, e.g., a liquid stream with air bubbles, is supplied via the inlet, the liquid passes through the hydrophilic membrane to an outlet while the gas passes through the hydrophobic membrane, which is in contact with the environment. Operation of the device, however, is highly dependent on its orientation with respect to gravity as well as the relative amounts of liquid and gas inside the chamber. In dependence of these factors, the hydrophilic membrane may only be in contact with gas while the hydrophobic membrane may simultaneously only be in contact with liquid. Since the hydrophilic membrane is, once wetted, non-permeable for gas and the hydrophobic membrane is non-permeable for liquid, neither of the liquid nor the gas can exit the chamber, resulting in a blockage. Therefore, the degassing device is not suited for an ambulatory infusion system that is carried by a person night and day and that may take any spatial orientation.
U.S. Pat. No. 6,347,711 B1 discloses a filter for medical fluids with a hydrophilic membrane and two hydrophobic membranes on opposes sides of the device, wherein one of the hydrophobic membranes is in a common plane with the hydrophilic membrane.